Digital subscriber line (DSL) technology was initially deployed to provide data-only service as a replacement for slower-speed, dial-up modems. Incumbent local exchange carriers (ILECs), competitive local exchange carriers (CLECs), and other telecommunication providers have begun to explore offering voice-over-Digital Subscriber Line (VoDSL) service, and other voice-over-broadband services, to deliver integrated voice and data services.
A central component of a typical VoDSL system is the voice gateway, or simply “gateway.” The gateway receives Voice over Internet Protocol (VoIP) or Voice over ATM (VoATM) information from the customer premises via network ports. The gateway then reformats the telecommunication information and sends it to a public switched telephone network (PSTN) via telecommunication ports. Likewise, telecommunication information from the PSTN is received at the telecommunication ports, packetized, and then transmitted to users via the ATM ports. Thus, the telephones, computers, and other telecommunication equipment at the customer premises are typically connected to the gateway via an ATM network, and the ATM ports in the gateway are wide area network (WAN) ports. The network ports typically reside on cards that plug in to the gateway. The network ports may, for example, connect to an ATM/IP network, a Digital Subscriber Line Access Multiplexor (DSLAM), or a Cable Modern Termination System (CMTS). Regarding specific techniques for encoding telecommunication information, there are several means available for carrying packetized voice over broadband, including the ATM Adaptation Layer Type 2 Broadband Loop Emulation Service (AAL2 BLES) protocol for carrying voice directly over ATM and the Voice over IP over ATM (VoIPoATM) protocol for transporting IP over ATM Adaptation Layer Type 5 (AAL5).
Gateways are now available with the capacity to process, bridge, and/or switch thousands of users. Network designers may also wish to oversubscribe the number of users based on statistical analysis of a network's behavior. In both cases, a large amount of user traffic passes through a typical gateway at any given time. Due to this large concentration of traffic, it is becoming increasingly important to maintain service, despite failure of components such as network ports.
One technique used to increase gateway reliability is to implement network port redundancy with automatic protection switching (APS). For conventional APS, the gateway is generally provided with at least one primary network port, known as the working port, and at least one redundant network port, known as the protection port. If the working port experiences a fault, the working port automatically passes the bearer traffic through to the protection port. Specifically, according to conventional APS, resources residing in the working port utilize a communication path that links the working port and the protection port to forward traffic received by the working port through to the protection port. Resources residing on the protection port receive the forwarded traffic and pass it through to the ATM network.
A disadvantage associated with this technique, however, is that additional resources must be provided on the network ports to support passing bearer traffic from the working port to the protection port. For example, the working port must include logic and hardware for detecting faults and forwarding traffic to the protection port. Thus, this method adds cost to the network ports. Furthermore, it may be necessary to remove the working port to cure the fault. However, removal of the working port will interrupt the bearer traffic that the working port passes through to the protection port unless additional steps are taken to otherwise reroute that traffic. There is therefore a need for improved protection-switching technologies that do not increase the cost of network ports and that allow working ports to be replaced easily without interrupting bearer traffic.